The invention relates to a process and equipment for the foam process web formation, and is related to U.S. Pat. No. 5,904,809, the disclosure of which is incorporated by reference herein.
In many applications of the foam process, a relatively high level of suction, e.g., on the order of about 1.5 meters of water, is provided as the primary web formation mechanism. However, for some products, it is desirable to provide a mechanical force and mechanical energy for removing the foam from the slurry to form a non-woven web so that the mechanical action provides more than 50% (typically more than 90%) of the web formation force. Under such circumstances nip rollers or like mechanical elements may be provided and the suction force utilized is relatively small, on the order 100 centimeters or less, typically less than 50 centimeters, e.g. about 10 centimeters of water head. There are many other features--such as various end seals, edge seals, former components, foam forming apparatus and methods, and the like--which also may desirably be utilized in order to make a wide variety of different products. According to the present invention a wide variety of alternative constructions and procedures are provided which allow great flexibility in implementing the foam process and the production of a wide variety of desired products, enhancing the utilization of the foam process as described in the above mentioned copending applications.
According to the first aspect of the invention a former assembly for producing a non-woven web of fibrous material is provided comprising the following components: A foraminous element (i.e. "wire") on which a non-woven fibrous web may be formed moving in a first direction. A former through which the foraminous element moves in the first direction, the former including a first foam/fiber slurry introduction end and a second formed web withdrawing end. Means for introducing a foam/fiber slurry into the former first end so that the slurry contacts the wire. Means for removing foam from the slurry to effect formation of a web on the wire wherein the wire has side edges substantially parallel to the first direction. An edge seal for each of the side edges of the wire which allows some sideways movement of the wire, in a dimension substantially perpendicular to the first direction, but does not allow significant leakage of slurry from the former. And means for introducing substantially fiber free foam into the edge seal at at least some portions thereof for providing lubrication and to assist in preventing leakage of fiber-containing slurry from the former.
The means for introducing the foam/fiber slurry may comprise any conventional structure for that purpose, including any type of conduit, header, manifold, nozzle, or the like which is suitable for that purpose. The means for removing the foam from the slurry to effect formation of a web on the wire may comprise suction tables, suction rollers, or the like, but preferably include at least one set of nip rolls. For example, the former may comprise a first section adjacent the first end including a suction table, and a second section adjacent the second end and comprising at least one set of nip rollers. The means for introducing substantially fiber-free foam into the edge seal preferably introduces substantially fiber-free foam only into the second section of the edge seal, not the first section, and the foam introduction means may comprise any conventional structure for that purpose including all types of conduits, nozzles, headers, manifolds, or like fluidic elements. The edge seal comprises a first edge seal at the first section, a second edge seal at the second section, and the second section may comprise at least two pairs of nips rolls with a suction device between the two pairs of nip rolls for handling foam removed by the nip rollers. Typically, the suction table in the first section will have low suction, less than 100 centimeters water head, preferably less than 50 centimeters water head, e.g. about 10 centimeters water head. The nip rolls provide more than 50% of the energy for foam removal to effect web formation, typically more than 90%, or any percentage between 51%-90%.
The nip rolls may have side faces and the second edge seal may comprise a plastic plate adjacent each side edge of the wire and associated with the nip roll side edges, and having a space formed therebetween. The foam introducing means introduces substantially fiber-free foam into the spaces so that substantially fiber-free foam fills the spaces. At least one of the nip rolls may comprise a suction roll for carrying away foam removed by the nip rolls, and a suction device between sets of nip rolls, or after the second nip rolls, typically is provided comprising either a low or high suction device; in any event the totality of all of the suction devices provide less than 50% of the energy for web formation.
The first edge seal may comprise a channel shaped element having a pair of substantially parallel metal side plates spaced from each other by a crosspiece, the side plates having outer surfaces receiving a wire edge therebetween and spaced from the wire. Flexible material sealing elements, such as O-rings (in strip form) or the like, of elastomeric material, may be stationarily mounted to the former and engage the side plate outer surfaces to provide a seal therewith. More than one set of O-rings may be provided to insure positive sealing. Also, any conventional means (such as pneumatic cylinders, reciprocating electrical motors or associated mechanical components or the like) are provided for reciprocating the crosspiece in a dimension substantially perpendicular to the first direction so as to accommodate wires of different width, but so that the side plates continue to engage the flexible material seals. That is, the side plates have a length greater than the length of travel of the reciprocating means to insure continued sealing.
Typically also provided are means for carrying foam removed by the foam removing means away from the removing means (such as conduits, associated pumps such as centrifugal pumps, or the like) into a device for mixing the additional fibers to produce a foam-fiber slurry (or "new" foam may also be added to the foam-fiber slurry). The device for mixing the foam with additional fibers may comprise a tank having a top, bottom, and a plurality of tangential foam inlets for establishing at least one vortex in the tank; means for adding fiber through the top of the tank (any conventional conveying or injecting structure, or any other structure for performing that function); and a foam-fiber slurry pump connected to the bottom of the tank. While the pump is preferably centrifugal, other types of pumps may also be utilized.
The former may further comprise a pivotal metal plate past which the wire moves, the plate having a free end a roller seal adjacent the free end and engaging the wire, with a volume defined between the free end and the roller seal. Means are preferably provided for injecting substantially fiber-free foam into the volume between the free end and the roller seal under a pressure greater than in the former on the opposite side of the roller seal from the free end. The foam injecting means may comprise any conventional structure for that purpose such as conventional conduits, pumps, nozzles, manifolds, or like fluidic components.
The former also further may comprise a rubber or plastic end portion comprising or covering in the free end of the pivotal plate. A second metal plate spaced from the pivotal metal plate and having a free end, a second roller seal spaced from the free end and engaging the wire, and another rubber or plastic end portion comprising or covering the second plate free end may also be provided.
The assembly according to the invention may also comprise means for introducing at least two different strata into the former at the first end thereof, the first of the strata comprising a fiber/foam slurry having first properties, and a second strata comprising a fiber/foam slurry having second properties significantly different from the first properties, or any other material capable of incorporation into a web of fibrous material (such as Sugar Absorbent Polymer--SAP, or other powders or slurries for performing particular functions). The strata introducing means may comprise any suitable conventional structure for that purpose including conventional manifolds, conduits, nozzles, and like fluidic components.
The assembly may also comprise means for reciprocating the strata introducing means toward and away from the former first end which allows adaptation of the process to particular strata and other parameters. The strata introducing means may also comprise at least one metal plate having a pivoted end most remote from the former first end, and a free end closest to the former first end, the free end having no metal portion touching the wire. In fact the wire may comprise a first wire and the assembly may further comprise a second wire moving generally parallel to the first wire, with the strata introducing means comprising a second pivoted plate and means for introducing at least three strata in the former first end. The first and third strata are typically in contact with the first and second wires (and the first and third strata typically being fiber/foam slurries of substantially the same properties and consistencies, although they may be different), with the second strata between the first and third strata which is thereby precluded from directly contacting the wires. Under these circumstances the second strata typically will be SAP or like material that must be prevented from coming into direct contact with the wires. The means for removing the foam from the slurry comprises, only in part, suction tables cooperating with the first and second wires adjacent the first end of the former, the tables supplying a vacuum of less than 100 cm water head (typically less than 50 cm water head, typically about 10 cm water head) so as to only remove excess foam from the slurry. The nip rolls downstream of the suction tables apply the majority of the force necessary for forming the web from the slurry.
According to a second aspect of the invention a former assembly for producing a non-woven web of fibrous material is provided comprising the following components: A foraminous element on which a non-woven fibrous web may be formed moving in a first direction. A former through which the foraminous element moves in the first direction, the former including a first foam/fiber slurry introduction end and a second formed web withdrawing end. Means for introducing a foam/fiber slurry into the former first end so that the slurry contacts the wire. Means for removing foam from the slurry to effect formation of a web on the wire. And wherein the former further comprises a pivotal metal plate past which the wire moves, the plate having a free end and a roller seal adjacent said free end and engaging the wire, a volume defined between the free end and the roller seal; and means for injecting substantially fiber free foam into the volume between the free end and the roller seal under a pressure greater than the pressure in the former on the opposite side of the roller seal from the free end. The details of the former, and other components, may be as described above.
According to another aspect of the invention a former assembly for producing a non-woven web of fibrous material is provided comprising the following components: A foraminous element on which a non-woven fibrous web may be formed moving in a first direction. A former through which said foraminous element moves in the first direction, said former including a first foam/fiber slurry introduction end and a second formed web withdrawing end. Means for introducing a foam/fiber slurry into said former first end so that the slurry contacts the wire. Means for removing foam from the slurry to effect formation of a web on said wire. And, means for introducing at least two different strata into said former at said first end thereof, a first of said strata comprising a fiber/foam slurry having first properties, and a second of said strata comprising a fiber/foam slurry having second properties significantly different from said first properties, or another material capable of incorporation into a web of fibrous material. The details of the means for introducing the strata, and the like structures, may be as described above.
According to yet another aspect of the invention relates to a method of forming a foam-fiber slurry having a solids consistency of between about 2-25%, utilizing a tank having an at least partially open top, a bottom, and an interior, said method comprising the steps of: (a) Tangentially introducing foam into the tank interior at a plurality of different locations spaced circumferentially around the tank interior, to form at least one vortex in the tank interior. (b) Introducing fibers into the tank through the open top thereof, to flow into the foam vortex and form a fiber/foam slurry having a consistency of between about 2-25%. And (c) pumping the formed slurry out of the tank through the tank bottom. Step (a) may be practiced utilizing 3-5 or more, tangential pipes extending into the tank, and fibers may be added from any suitable conventional conveying structures for fibers, for example, simply falling through the open top of the tank into the tank interior. The fibers may be of any conventional cellulose or non-cellulose configuration and construction, as described in the copending applications mentioned above, and the consistency may be within any narrow range within the 2-25% range set forth above, e.g. between about 3-20%, between about 5-10%, etc. Pumping may be accomplished utilizing a centrifugal pump, or any other conventional type of pump, and pumping may take place directly to a manifold which distributes the fiber/foam slurry to two or more different conduits for utilization of the structures. The foam that is utilized in the practice of step (a) may be foam that is recycled after having been withdrawn during the earlier web formation and/or may include newly created foam.
It is a primary object of the present invention to provide versatile assemblies and methods for employing the foam process of non-woven web formation in order to facilitate a wide variety of web formations. This and other objects of the invention will become clear from an inspection of a detailed description of the invention, and from the appended claims.